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UBC Theses and Dissertations

Determination of the antibiotic resistance and bacteriophage infectivity of verocytotoxigenic Escherichia coli Ma, Yvonne Yan Hon


Verocytotoxigenic Escherichia coli (VTEC) are bacteria that have been implicated in foodborne outbreaks, and may be transmitted to food by contaminated irrigation water. Antibiotics are not generally used in VTEC infection treatment, however the presence of antimicrobial resistant (AMR) bacteria and genes in the environment pose a threat to human health due to the potential for horizontal gene transfer. The broth microdilution technique was used to determine if VTEC strains (n = 15) isolated in 2014-2016 from irrigation water in British Columbia (BC) were resistant or susceptible to the following antibiotics: ampicillin, ceftriaxone, chloramphenicol, gentamicin, nalidixic acid, streptomycin, trimethoprim-sulfamethoxazole, and tetracycline. Compared to VTEC isolated from 2012-2013, strains from 2014-2016 had overall lower rates of antibiotic resistance. Whole genome sequences of VTEC strains (n = 67) isolated from 2012-2016 were queried against the ResFinder database and acquired AMR genes such as aph(3”)-Ib, aph(6)-Id, blaTEM-1b. dfrA8, sul2, tetA and tetB were identified in antibiotic resistant VTEC. Bacteriophages (phages) are viruses that use bacteria as a host cell, and their use as an antimicrobial against pathogens has been examined. Phages (n = 15) that target VTEC were isolated from sewage and their spotting host range was determined. Further characterization of four VTEC phages was done to determine if they had characteristics that are suitable for use in the food industry. The four phages had similar morphology to the Myoviridae family from transmission electron microscope images, had latent periods ranging from 35-55 minutes, burst sizes ranging from 15 to 57 phages per cell, and were stable over 31 days at pH 8, 10 and at 4°C, varied stability at pH 6 or at -20°C or 22°C, and not at pH 2, 4 or at 37°C. The potential for Salmonella phages (n = 34) to infect VTEC was examined by the spotting and plaquing host range assays. Nine Salmonella phages were capable of lysing VTEC, however only six were able to form plaques on VTEC. This research provides insights into AMR patterns in VTEC isolated from irrigation water in BC, and about novel phages for potential use for VTEC biocontrol in the food industry.

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